1. Field of the Invention
The present invention relates in general to a method of obtaining particulars or characteristics of an ophthalmic lens by detecting a fluorescent light which is emitted from the ophthalmic lens upon exposure to an excitation light (UV light). The particulars or characteristics of the ophthalmic lens include, for instance, identifying marks such as characters, figures, symbols, etc. which are formed in the ophthalmic lens to identify the ophthalmic lens, a thickness of the ophthalmic lens such as a contact lens and an intraocular lens, and an angular position of the ophthalmic lens, particularly of a special contact lens having circumferential portions having respective different thickness values.
2. Discussion of Related Art
As one example of the particulars or characteristics of an ophthalmic lens which give information on the lens, there are known identifying marks formed in predetermined portions of the ophthalmic lens such as a contact lens or an intraocular lens. The identifying marks include characters, figures, symbols and others, which permit or facilitate a differentiation between front and back surfaces of the lens or between lenses for left and right eyes. Further, the identifying marks are formed to indicate the thickest circumferential portion in the lens or specifications of the lens and manufacturing information such as a manufacturer's name. For marking the ophthalmic lens, a laser radiation is used to engrave the identifying marks in the lens surface, or a printing liquid containing a pigment or a dye is used.
The identifying marks formed in the ophthalmic lens as described above are checked or read upon packaging or shipment of the lens by a worker, for assuring delivery of a lens suitable to a specific user, or distinguishing various types of lenses from each other in the production line. In general, the identifying marks are manually checked by the worker for each of a plurality of ophthalmic lenses, by visually inspecting each lens directly or through a magnifying glass. Since the identifying marks are formed generally at a peripheral portion of the lens for the purpose of avoiding an adverse influence on its optical region, it is rather difficult to recognize the identifying marks by the worker's visual inspection. Accordingly, the conventional method of reading the identifying marks by the worker's visual inspection undesirably suffers from reading errors of the identifying marks due to sensory errors and fatigue of individual workers. Further, the production efficiency of the lens is undesirably deteriorated.
In view of a current trend that disposable contact lenses are widely used, there is a demand for mass-production of the ophthalmic lens with high production efficiency at a reduced cost. The above-described conventional method of manually reading the identifying marks by the worker's visual inspection, however, does not meet the demand.
As one technique for solving the problem described above, it is proposed to take an image of the marked ophthalmic lens by a CCD camera, for instance, and to process the obtained image by an image data processing device. In this technique, however, it is difficult to obtain a sufficiently clear image of the lens for reading the identifying marks since the ophthalmic lens is transparent and the identifying marks formed in the lens are transparent or pale in color.
U.S. Pat. No. 6,124,594 discloses a method of confirming the presence of a contact lens in a package by using an infrared radiation. JP-A-2000-177720, JP-A-11-503232, and JP-A- 9-504095 disclose a method of detecting the presence of a contact lens in a container, or a method of detecting defects of a contact lens such as scratches and chips, comprising the steps of applying an excitation light such as a UV light to the contact lens, and taking a fluorescent image of the lens while the lens is emitting a fluorescent light by exposure to the excitation light. None of the methods, however, disclose or suggest reading the identifying mark formed in the lens by utilizing the fluorescent image. Accordingly, the identifying mark needs to be read manually by the worker's visual inspection, thereby causing a risk of delivering, to a user, improper lenses having the specifications such as the optical power and the radius of curvature, which are different from those suitable to a specific lens user.
It is therefore a first object of the present invention to provide a method of accurately and easily reading an identifying mark formed in an ophthalmic lens so as to obtain information on the lens, so that the obtained information are compared with prepared reference information for the purpose of distinguishing various types of lenses from each other in the production line.
Another example of the particulars which give information on the ophthalmic lens, the thickness of the ophthalmic lens, especially at its optical center, is measured. For providing a lens user with an ophthalmic lens suitable to an eye of the lens user, and for effectively practicing a quality inspection and an inventory control of the ophthalmic lens, it is required to measure the optical center thickness of the ophthalmic lens. There are proposed various methods for measuring the optical center thickness of the ophthalmic lens, especially a contact lens, for example, methods which use contact members, an ultrasonic wave, and an optical microscope.
For instance, a dial gauge or indicator which includes a pair of contact members is used for measuring the optical center thickness of the ophthalmic lens. The contact members are brought into contact with central portions of the opposite surfaces of the ophthalmic lens, respectively, so that the optical center thickness of the ophthalmic lens between the contact members is measured. In this contact-type method wherein the contact members are held in contact with the ophthalmic lens, there is a risk that the contact members may scratch or damage the ophthalmic lens surface. Further, since it is difficult to accurately determine a position of the lens at which the thickness should be measured, the thickness cannot be measured at a desired portion every time when the ophthalmic lens is subjected to the measuring operation, undesirably causing measuring errors. Where the contact members having a relatively large diameter are used to measure the optical center thickness of a toric lens or a bifocal lens whose optical center is offset from a geometrical center, it is difficult to bring the contact members into accurate abutting contact with the desired circumferential portion of the lens whose thickness varies in the circumferential direction. In this case, the optical center thickness of the ophthalmic lens cannot be accurately measured.
When the optical center thickness of the ophthalmic lens is measured by using the ultrasonic wave, the ultrasonic wave generated from an ultrasonic wave transducer is applied to the ophthalmic lens along an axis passing the center of the spherical surface of the lens. The optical center thickness of the ophthalmic lens is obtained from the waves which are respectively reflected by the opposite surfaces of the lens. Unlike the above-described method using the contact members, this method permits the measurement of the optical center thickness of the lens in a non-contact manner without using any members in contact with the lens surface. This method, however, requires a relatively long period of time for the thickness measurement and an accurate temperature control, inevitably pushing up the cost of the measuring device.
When the optical center thickness is measured by using the optical microscope, it is generally impossible to measure the thickness of the ophthalmic lens with the lens being immersed in a liquid such as water, due to attenuation of a light. A soft contact lens, in particular, is likely to be deformed due to evaporation of the aqueous component therefrom during the measuring operation, whereby the thickness of the lens cannot be accurately measured.
It is therefore a second object of the present invention to provide a novel method of easily and accurately obtaining a thickness of an ophthalmic lens in a non-contact manner without using any members in contact with the lens surface, for thereby avoiding a risk of damaging the ophthalmic lens.
As another example of the particulars which give information on the ophthalmic lens, an angular position of the ophthalmic lens is detected. The angular portion of the ophthalmic lens is detected for the following reasons.
As a contact lens for vision correction of an eye suffering from deteriorated accommodation such as presbyopia and astigmatism, there is proposed a special contact lens having circumferential portions having respective different thickness values. The special contact lens includes a toric lens having a toric shape, and a multifocal lens such as a bifocal lens having a plurality of vision correction powers.
The special contact lens such as the astigmatism correction contact lens or the presbyopia correction contact lens providing near and distant vision correction powers is positioned on an eye of the lens wearer with a predetermined circumferential orientation thereon while being prevented from rotating in the circumferential direction. As one technique for positioning the lens on the lens wearer's eye with a predetermined circumferential orientation, a prism ballast mechanism is generally known. The contact lens which employs the prism ballast mechanism has a gravity center at a relatively lower portion thereof, by offsetting the centers of front and back surfaces from each other by a suitable offset amount, with the thickness of the lower portion being increased. Therefore, the contact lens can be placed on the eye while maintaining the desired circumferential orientation. In the contact lens with the prism ballast mechanism described above, the lower portion thereof has a thickness larger than the other portion when placed on the eye with the desired circumferential orientation.
For an effective quality inspection and an inventory control of the special contact lens described above, there are conducted various examinations on the special contact lens for obtaining the characteristics thereof. In the astigmatism correction contact lens, for instance, a spherical power, a cylindrical power, an orientation of an astigmatic axis, and an amount of prism are examined. The presbyopia correction contact lens is examined, for instance, for the circumferential positions of areas or regions to which a distant and a near vision correction power and an additional power are given. Prior to these examinations, it is necessary to clarify or specify a position of a reference circumferential portion at which the thickness of the lens is the largest. In other words, it is necessary to detect a reference radial direction which is defined by a geometrical center of the lens and the reference circumferential portion having the largest thickness.
For detecting the reference radial direction described above, a suitable index or a mark is formed on the surface of the special contact lens at a circumferential position corresponding to the reference circumferential portion having the largest thickness. In conducting various examinations, the index of the lens is positioned in the circumferential direction with a suitable inspecting device. However, the manual positioning of the index of the contact lens with the inspecting device inevitably causes a positioning error, and requires a relatively long period of time for detecting the reference radial direction.
Even if the reference radial direction were appropriately recognized, the cost of producing the contact lens would be undesirably increased due to forming the index on the lens surface. Further, if the index is erroneously positioned on the lens surface, that is, the index is offset from the actual reference portion, the reference radial direction is inevitably determined based on the erroneously positioned index.
It is therefore a third object of the present invention to provide a novel method of easily and accurately detecting an angular position of an ophthalmic lens, particularly, a special contact lens having different thickness values at different circumferential positions, without forming any identifying marks or indices on the surface of the lens. The angular position of the lens is defined, for instance, by a position of the thickest circumferential portion (the above-described reference circumferential portion) of the lens, i.e., the reference radial direction.